In the technical report entitled “A Low Supply Voltage High PSRR Voltage Reference in CMOS Process” by Khong-Meng Tham and Krishnaswamy Nagaraj, a conventional bandgap reference voltage circuit 10 is disclosed, as shown in FIG. 1(a). The bandgap reference voltage circuit 10 includes a first, a second and a third p-typed metal oxide semiconductor field effect transistors (MOSFETs) M1, M2 and M3, a first and a second pnp-typed bipolar junction transistors (BJTs) Q1 and Q2, and a first and a second resistors R1 and R2. In this case, the pn junction area ratio of the first pnp-typed bipolar junction transistor Q1 is equal to M multiplied by that of the second pnp-typed bipolar junction transistor Q2, in which M is an integer greater than 2, and the channel area ratio of the third p-typed metal oxide semiconductor field effect transistor M3 is equal to N multiplied by those of the first and the second p-typed metal oxide semiconductor field effect transistors M1 and M2, wherein the respective channel areas of the first and the second MOSFETs, M1 and M2 are the same so as to constitute a current mirror.
Through the simple algebra operation, the bandgap voltage VBG is presented as the following equation (1).VBG=VBEQ2+N(R2/R1)1n{M(N+1)}VT  (1)
Because the characteristics that the base-emitter voltage of the second bipolar junction transistor Q2 would decrease with the rising temperature (about −2.2 mV/° C. at 25° C.) and that thermal voltage constant would increase with the rising temperature (+0.085 mV/° C.), thus a bandgap reference voltage VBG which is independent of temperature is achievable via selecting suitable values of the ratio of R2 and R1, M and N.
However, the disadvantage of the bandgap reference voltage circuit 10 shown in FIG. 1(a) is that the voltage VREG would decrease with the rising temperature while the bandgap reference voltage VBG still remains as a constant, which makes the source-drain voltage VSD of the third metal oxide semiconductor field effect transistor M3 decrease substantially. When the temperature reaches a specific value, the third metal oxide semiconductor field effect transistor M3 would be operated in a triode region, as shown in FIG. 1(b). This makes the drain current ID of the third metal oxide semiconductor field effect transistor M3 decrease instantly and the bandgap reference voltage VBG would substantially decrease with the rising temperature responding thereto, which leads to a failure situation on the temperature compensation effect, as shown in FIG. 1(c).
For overcoming the mentioned disadvantage of prior art above, a novel bandgap reference voltage circuit is provided in the present invention. The provided bandgap reference voltage circuit is capable of performing the temperature compensation effect normally so as to provide a stable bandgap reference voltage.